1. Field of the Invention
This invention relates to a method and apparatus for preparing a liquid mixture of liquid carbon dioxide and a liquid chemical soluble in liquid carbon dioxide; to a method and apparatus for producing a flow of such liquid mixture; and to a method and apparatus for producing a flow of carbon dioxide gas containing vapor of such liquid chemical.
2. Discussion of the Background
Carbon dioxide is used as an attracting agent for removal trapping or destructive sampling of biting insects. The use of carbon dioxide together with certain other chemical compounds, for example, acetone or octenol, produces a synergistic effect greatly increasing the trapping results for certain insects.
Carbon dioxide is available as a liquified gas under its own vapor pressure of 5.7 MPa at 20.degree. C. in standard high pressure vessels containing 9 to 23 kg of carbon dioxide. Liquid carbon dioxide is also available from low pressure, insulated bulk vessels, where the pressure is kept low by maintaining the temperature at a suitable low level with a mechanical refrigeration unit. Low pressure vessels are available in capacities of 2,720 kg, 3,630 kg, 5,440 kg, 11,800 kg, 21,800 kg and 28,100 kg.
Liquid carbon dioxide is a very good solvent for many chemical compounds. This property is used to extract and recover chemical products from natural and synthetic mixtures. Acetone, for example, is completely soluble in liquid carbon dioxide. The solubility of octenol in liquid carbon dioxide is about 5% by weight.
Homogeneous mixtures of acetone or octenol in liquid carbon dioxide can be prepared in high or low pressure vessels provided the concentrations are kept below the solubility limits.
Currently, mixtures of acetone or octenol in carbon dioxide are prepared dynamically by metering a flow of gaseous carbon dioxide from a standard vessel and mixing it with acetone or octenol vapor obtained by evaporation from a wick in a liquid reservoir. The acetone or octenol concentration depends on the reservoir temperature, state of the wick and the stability of the carbon dioxide flow.
Homogeneous gas mixtures of acetone or octenol in gaseous carbon dioxide can be prepared in a vessel provided that the final pressure is below the vapor pressure of the carbon dioxide or the acetone or octenol, at the minimum exposed temperature of the vessel. This is to eliminate condensation of any component of the mixture. The final pressures are so low that the quantity of the mixture available from the vessels is very small.
Liquid mixtures of acetone or octenol in carbon dioxide would provide an easy method to store and to deliver the required quantities of homogeneous gas mixture, by using liquid withdrawal and followed by vaporization.